Many research institutions are currently conducting research to develop Silicon Carbide (SiC) devices, and Gallium Nitride (GaN) devices. Advantages of power devices and GaN power devices over conventional Si power devices include high breakdown voltage, low on resistance, high switching speed, high temperature operation, etc.
Since such new materials devices have comparatively low threshold voltage, and Cgs/Cgd is comparatively small, where Cgs is a capacitance between the gate and the source, and Cgd is a capacitance between the gate and the drain, a remarkable effect may be given, by time differential dVds/dt of the voltage Vds between the drain and the source, to voltage Vgs between the gate and the source via the capacitance Cgd between the gate and the drain. Accordingly, it is easy to be erroneously turned on.
In particular, since Cgs/Cgd is comparatively small in the case of horizontal GaN based High Electron Mobility Transistors (HEMT), vertical GaN based high electron mobility transistors, and SiC Trench Metal-Oxide-Semiconductor Field Effect Transistors (TMOSFET), a remarkable effect may be given, by time differential dVds/dt of the voltage Vds between the drain and the source, to voltage Vgs between the gate and the source via the capacitance Cgd between the gate and the drain, and thereby it is easy to be erroneously turned on.
It is also caused by operating conditions of new materials devices being high voltage and high speed driving.
If transistors are driven at high voltage or at high speed, the voltage Vds between the drain and the source and the drain current Id will be largely changed. As a consequence, time differential dVds/dt and dId/dt is increased. Accordingly, this is fed back to the capacitance Cgd between the gate and the drain, and thereby causes rise of the voltage Vgs between the gate and the source.
It is effective to reduce the gate resistance in order to prevent such phenomenon, while it is traded off in a circuit which needs to reduce surge voltage by the gate resistance.